Metallic foreign object detector, wireless power transmitting device, wireless power receiving device, and wireless power transmission system

A metallic foreign object detector for a wireless power transmission system comprising a feeding side resonance circuit and a receiving side resonance circuit, the feeding side resonance circuit including a feeding coil and a feeding side capacitor, the receiving side resonance circuit including a receiving coil and a receiving side capacitor, the metallic foreign object detector comprising:

• an antenna coil disposed between the feeding coil and the receiving coil;
• a capacitor that constitutes a resonance circuit together with the antenna coil;
• a drive part that applies voltage to the resonance circuit to generate a vibration signal in the resonance circuit;
• a determination part that determines a presence/absence of a metallic foreign object based on a waveform of the vibration signal;
• a first switch inserted into the resonance circuit;
• and
• a control part that controls an open/close state of the first switch,
• wherein the control part brings the first switch into a closed state responding to the drive part starting application of voltage to the resonance circuit, and
• wherein the antenna coil and the capacitor are included in the metallic foreign object detector independently of the feeding coil, the feeding side capacitor, the receiving coil, and the receiving side capacitor.